The present invention relates to the electronic storage of data, more specifically to an associative memory. Associative memories including so called content-addressable memories have been proposed, which are digital data storage devices, in which digital data are stored in the form of data patterns or "words" comprising a series of data elements, as bits or bytes. The data can be retrieved by addressing the associative memory with an input word or part of it. Depending on the type of storage, the input word may be the data word itself or a word differing from the stored word. The output of the memory comprises the addressed stored data word but possibly also words associated with more or less similar input words, if an incomplete or partially wrong input word is used for retrieval. This flexibility is achieved by time-consuming serial search algorithms.
Another known type of associative memory does not rely on serial search procedures but uses the storage of correlations. Recent research has shown that the data word storage capacity of such an "associative correlation memory" is only a factor of about 2 less than to that of a conventional listing memory, such as a random access memory (RAM) or a conventional associative memory having the same number of memory cells or storage locations, if the data words used comprise relatively few NON-ZERO data elements compared with the total number of data elements in a data word, see e.g. G. Palm, "On Associative Memory", Biol. Cybernetics 36, 19-31, 1980. On the other hand, associative and especially correlation memories have many and important advantages over listing memories, such as RAM's, as is well known to those skilled in the art.